The invention generally relates to voltage to current converters and, more particularly, to a voltage to current converter configured with variable transconductance (Gm).
Voltage-to-current converters are implemented in many conventional applications. Related transconducting devices are electronic building blocks characterized by a current output derived from a voltage input in a linear relationship Iout=Gm*Vin, where Gm is transconductance, and where Seimens (S) is the standard unit of Gm in Amps/Volt. Voltage-to-current converters form the basic input structure of instrumentation amplifiers and are used as basic Gm building blocks in frequency shaping devices. Generally, the value of Gm in a conventional voltage to current converter is fixed and is determined by the circuit elements. Thus, the Gm is fixed when the circuit is manufactured. It is possible, however, to vary the Gm using programmable means on a circuit chip. In such a configuration, the Gm could be varied by such programmable means according to a run-time configuration, rather than a predetermined configuration. These devices are used in programmable linear filters, gain amplifiers and other general purpose linear processing elements. Such transconducting devices, being building blocks of fixed and programmable components, have a large impact on the performance of the device in which they are incorporated. Conventional devices are limited in the manner and quality in which the Gm value is set or otherwise programmed. Performance factors such as the accuracy with which the Gm is set, the range over which the Gm is set, the resolution over which the Gm is set, and the linearity of the Gm at a particular point are all factors that affect the performance of the Gm device. Therefore, improving these factors in a Gm device would improve the device's performance, as well as the component or other device within which it is incorporated. Therefore, there exists a need for Gm devices having improved performance factors. As will be seen below, the invention accomplishes improved performance factors in an elegant manner.